FIG. 9 is a block diagram showing a configuration of a radio monitoring system 1 of related art. The radio monitoring system 1 of related art includes a plurality of image monitors 2, and a plurality of TV cameras 3 disposed away from the image monitors 2. Image information of an image taken by each of the TV cameras 3 is displayed on the image monitor 2, whereby a user can grasp the image information of a remote place. Such radio monitoring system 1 includes a plurality of TV cameras 3, a plurality of secondary stations 4 provided for the TV cameras 3, respectively, a plurality of image monitors 2, and a plurality of primary stations 5 provided for the image monitors 2, respectively (see e.g. Japanese Unexamined Patent Publication JP-A 9-163355 (1997)).
The secondary stations 4 send the primary stations 5 signals for confirming whether or not sending of image signals is requested, and receive reply signals to the confirming signals. In this way, the primary station 5 to be sent image signals can be ascertained. Each of the secondary stations 4 sends image signals to the primary station 5 which has requested image signals. On receipt of image signals, the primary station 5 provides image information presented by the received image signals to the image monitor 2 thereby to make the image monitor display the image information. According to the above procedures, the particular image monitor 2 can be made to display image information presented by image signals taken by the particular TV camera 3.
However, there is a problem that the secondary stations 4 consume a larger power because the secondary stations 4 send a signal for confirming whether or not the primary stations 5 have made a request for sending of image signals for the purpose of ascertaining whether or not the primary stations 5 have made a request for sending of image signals. Further, in the case where the primary stations 5 send a signal showing whether or not they have made a request for sending of image signals out of synchronization with the secondary stations 4, the secondary stations 4 need to be kept ready to receive the signal at all times, which poses a problem that the secondary stations 4 consume a larger power.